The term 'spineless one' can be defined by four crossword solutions: WORM (4 letters), JELLYFISH (9 letters), WIMP (4 letters), and SISSY (5 letters). A WORM is a small, segmented invertebrate that lives in soil or water. JELLYFISH are aquatic invertebrates with a gelatinous body and tentacles. A WIMP is a person who is weak and cowardly. A SISSY is a person who is overly timid or cowardly. All of these terms refer to someone who is spineless, or lacking courage.