to weigh in the mind; to consider carefully
• (v. i.) To attend; to be attentive. • (v. t.) To weight carefully in the mind.
(perpendicular end) vertical cross joint in stone or brickwork. Perpends also refer to the ends of walls first built up by bricklayers to provide a level for the courses in between. See brick/brickwork and racking back. 
In masonry the vertical joints. From perpendicular. Commonly called Perps; 
Per·pend' intransitive verb To attend; to be attentive. [ R.] Shak. Per·pend' transitive verb [ Latin perpendere , perpensum ; per + pendere to weight.] To weight carefully in the mind. [ R.] ' Perpend my words.' Shak.