An Etymological Dictionary of the German Language/Haff
Haff, n., ‘inland sea, gulf,’ a LG. word, orig. ‘sea’ (generally), which is also the meaning of AS. hœf (plur. heafu), n., Scand. haf, n., MidLG. haf; the UpG. words, MidHG. hap, habes, n., and habe, f., which correspond in sound, also signify ‘sea,’ as well as ‘port’ (see Hafen). As we need not assume an orig. difference between the words for ‘harbour’ and ‘sea,’ and since in any case the meaning ‘harbour’ is derived from the signification ‘sea’ — the converse would be hardly possible — the usual assumption mentioned under Hafen (2.), that Hafen is lit. ‘receptacle,’ is quite problematical. Hence Hafen may probably be explained by some such word as ‘marina,’ in the sense of ‘statio marina.’ The connection of AS. hœf, ‘sea,’ as ‘heaving,’ in the sense of Lat. altum (‘high sea’), with heben (root haf, pre-Teut. kap), is not impossible, though scarcely probable.