The word "unmasculine" suggests a lack of traditional male characteristics such as strength, bravery, and toughness. For those looking for synonyms, there are several to choose from. "Effeminate" implies a feminine quality to a person. "Unmanly" also suggests a lack of traditional male qualities. "Timid" suggests a lack of courage or boldness. "Weak" implies a lack of strength. "Spineless" suggests a lack of strength of character or resolution. "Unheroic" implies a lack of bravery or heroic qualities. Ultimately, the specific synonym chosen will depend on the context in which it is being used and the specific nuances one wants to convey.