1) in exchange for (only construct) prep 2) in return for
Full Brown-Driver-Briggs lexicon entry
I. חֵ֫לֶףnoun [masculine]exchange, only construct, as preposition in return for (so הֲלַף, , common in Aramaic e.g. Gen 4:23ᵑ7ᵑ6 for Hebrew תַּחַת) — עֲבֹדָתָם׳ח (עֲבֹדַתְכֶם) Num 18:21; Num 18:31 (both P).