delay, procrastinate, lag, loiter, dawdle, dally mean to move or act slowly so as to fall behind.

delay usually implies a putting off of something (such as a beginning or departure).

procrastinate implies blameworthy delay especially through laziness or apathy.

lag implies failure to maintain a speed set by others.

loiter and dawdle imply delay while in progress, especially in walking, but dawdle more clearly suggests an aimless wasting of time.

dally suggests delay through trifling or vacillation when promptness is necessary.