[joist] n [ME joiste, fr. MF giste, fr. (assumed) VL jacitum, fr. L jacere to lie--more at adjacent] (15c): any of the small timbers or metal beams ranged parallel from wall to wall in a structure to support a floor or ceiling
JOIST
Meaning of JOIST in English
Merriam-Webster English vocab. Английский словарь Merriam Webster. 2012