joist (joist) n. Any of the wood, steel, or concrete beams set parallel from wall to wall or across or abutting girders to support a floor or ceiling. tr.v.
joist·ed, joist·ing, joists To construct with joists.
[Middle English giste, joiste, from Old French giste, from feminine past participle of gesir, to lie, lie down, from Latin iacēre; see yē- in Indo-European roots.]
1375 (attested from 1294 in Anglo-L.), from O.Fr. giste "beam supporting a bridge" (Mod.Fr. gîte), noun use of fem. pp. of gesir "to lie," from L. jacere "to lie, rest," related to jacere "to throw" (see jet (v.)). Notion is of wooden beam on which boards "lie down."