lukewarm (adj.)

• aestival
• apathetic
• chilly
• cold
• cool
• equatorial
• genial
• half-baked
• halfhearted
• hesitant
• indecisive
• indifferent
• insouciant
• irresolute
• lackadaisical
• mild
• neuter
• neutral
• nonchalant
• nonobservant
• perfunctory
• phlegmatic
• subtropical
• summery
• sunny
• temperate
• tepid
• thermal
• thermic
• tropical
• uncertain
• uncommitted
• undecided
• undutiful
• unenthusiastic
• unfrozen
• unmoved
• unresolved
• unresponsive
• warm
• wishy-washy