joist 
(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 the Appendix of Indo-European roots.]