(of a person) Late, tardy, overdue, behind (in accomplishing a task, etc.).
(of a task or the object of a task) Not at the expected point of completion.
Behind (someone or something moving, a trend, etc.), lagging behind, not keeping up.
Behind in paying a debt; in arrears.
Not having enough of, lacking (in something).
Inferior, less advanced (compared with someone in something).