The headword, neuter nominative/accusative singular of this adjective, occurs 26 times in Homer, as a formulaic epithet for a spear: 'casting a long shadow'. (For the 'long' part of the compound cf. delta 1336, delta 1337, delta 1338, delta 1339.)
The Suda's gloss on it here is unparalleled, but makra\n poreuo/menon in a scholion on Homer, Iliad 3.346 (web address 1) and ps.-Zonaras comes closest. See also e.g. Hesychius delta2151.