Architectural and Engineering Glossary


Laundry Tray, Laundry Tub, Set Tub

A deep wide sink or tub,usually of porcelain,slate,or soapstone;used for washing clothes,etc.


On drawings,abbr.for lavatory.


In monasteries of the Middle Ages,a large stone basin from which the water flowed through a number of small orifices around the edges,for the convenient performance of ablutions before religious exercises or meals.


A place for washing.


1.A Greek Orthodox monastery.2.In a monastery,an assemblage of cells for monks around a common center that contains a church and sometimes a refectory.

Law Of Reflection

As applied to rays of light, sound,or radiant heat which strike a surface:the angle of reflection is equal to the angle of incidence,and the reflected and incident rays are in the same plane with a perpendicular to the surface.


1.An open space of ground of some size,covered with grass and kept smoothly mown.2.Same as gauze,2.

Lawn Sprinkler System

A system of devices,usually installed below ground level,to scatter or spray water droplets over a lawn,golf course,or the like.

Lay Bar

A horizontal glazing bar.

Lay Board

A board which is fixed on the rafters of a pitched roof to take the feet of the rafters,forming a subsidiary roof transverse to the main roof.

Lay Panel

A wall panel whose horizontal dimension is greater than its vertical dimension. 


1.In reinforced plastics,the reinforcing material placed in position in the mold.2.The resin-impregnated reinforcement.3.The assem bling of veneers for fabrication as plywood.


Same as course.

Layer Board

Same as lear board.


See lath laid-and-set.

Laying Length

The length of an installed pipeline,measured along its centerline.

Laying Off

The elimination of roller marks or brush marks on a wet paint surface by the application of light brush strokes.

Laying Out

The marking of a material,indicating where cuts are to be made,in preparation for work to be done

Laying To Bond

Laying all the bricks in one course without the use of a cut brick.

Laying-off Angles

In surveying,rotating a level to measure the angle between two intersecting lines.


A glazed opening in a ceiling to admit light (either natural or artificial) to a room below. 

Lazaret, Lazarette, Lazaretto, Lazar House

A segregated area for infectious medical patients,esp.for their quarantine.

Lazy Susan

A circular,revolving shelf;some times used in corner kitchen cabinets.


Abbr.for “pound.”


Abbr.for lumber.


1.Abbr.for light center length.2.Abbr.for “less than carload.”


Abbr.for loose cubic meter.


Abbr.for loose cubic yard.


On drawings,abbr.for landing.

Le Chatelier Apparatus

A device used in the testing of hydraulic cements to measure soundness.


1.The process of separating a liquid from a solid (as in waste liquid) by percolation into the surrounding soil.2.The process of allowing soluble nutrients to move downward and percolate through the surrounding soil.

Leaching Basin

A drainage pit with sand and gravel sides constructed to allow water to dissipate.

Leaching Cesspool

A cesspool,1 in which the solids present are retained and the liquid seeps into the surrounding soil.

Leaching Field

Same as absorption field.

Leaching Pit

See leaching well.

Leaching Well, Leaching Pit

A pit,or a receptacle having porous walls,which permits its liquid contents to seep into the ground,but retains the solids.


1.One of the sections of a masonry wall built up at each corner;supports a line between them which serves as a guide for constructing the remainder of the wall.2.(pl.) See leads.3.A soft, malleable,heavy metal;has low melting point and a high coefficient of thermal expansion;very easy to cut and work.

Lead Bat

See lead wedge.

Lead Burning

The welding of sheet lead.

Lead Chromate

One of a series of opaque pigments,orange to yellow in color,with high tinting strength.

Lead Damp Course

A damp course fabricated of sheet lead.

Lead Dot

A device for fastening sheet lead to a stone surface.

Lead Drier

One of many organic lead salts which are soluble in paints and varnishes;used  to speed the drying and hardening of the oil vehicle.

Lead Flat

A flat roof which is covered by lead sheet laid over boarding.

Lead Foil Tape

A tape,typically about 1⁄2 inch wide and 0.002 inch thick (12.5 mm 0.05 mm),which is cemented to a window or panel to detect its breakage;forms part of an alarm circuit through which a small electric current flows.If the window or panel is broken,the tape is severed and the circuit is interrupted,thereby activating an alarm.

Lead Glazing

A leaded light.

Lead Head Nail

A roofing nail having a plain shank;makes a leakproof joint when driven through a metal roof.

Lead In Oil

White lead ground in linseed oil;formerly in wide use,now replaced largely by titanium dioxide pigments.

Lead Joint

A joint in a water pipe in which molten lead has been poured,as in a bell and spigot joint.

Lead Monoxide

Same as litharge.