From a later form of ithand, itself an alteration (due to assimilation to suffix -and) of Middle English ithen, from Old Norse iðinn ("assiduous, diligent"), from iðja, iðna, from ið, equivalent to ithe + -and and/or ithe + -en. Cognate with Icelandic iðinn ("diligent"), Norwegian idig ("busy"), Danish id ("pursuit, calling, business"). More at ithand.