There are several synonyms for the phrase "without enthusiasm," including lackluster, uninspired, unenthusiastic, apathetic, indifferent, and spiritless. Each of these words implies a lack of enthusiasm, energy, or excitement in a given situation. Lackluster suggests a dull or uninspiring performance or effort, while uninspired implies a lack of creativity or originality. Unenthusiastic means a lack of enthusiasm or interest, while apathetic suggests a profound indifference or disinterest in something. Indifferent conveys a lack of concern or interest, while spiritless denotes a lack of vitality or vigor. Overall, these synonyms for "without enthusiasm" all suggest a lack of passion, energy, or excitement.