From Middle English forthnimen, equivalent to forth- + nim. Compare Dutch voortnemen (“to continue to take”), German fortnehmen (“to take away”).
forthnim (third-person singular simple present forthnims, present participle forthnimming, simple past forthnam or forthnimmed, past participle forthnum, forthnumb or forthnimmed)
- (transitive, obsolete) To take away; destroy.
- (intransitive, obsolete) To go away.