'cluster-flowering' originates from Modern English as a compound of 'cluster' + 'flowering', formed by combining 'cluster' (a group or bunch) with 'flowering' (the act or state of producing flowers).

'cluster' entered Middle English from Old North French/Old French influences (Middle English forms include 'clustre'/'clustere'), and 'flower' comes from Old French 'flor'/'flour' (from Latin 'flōs'). The compound 'cluster-flowering' is a later Modern English formation combining these elements.

Initially the parts meant 'a bunch or group' ('cluster') and 'the act/state of producing flowers' ('flowering'); combined in Modern English they specifically describe the way flowers are arranged (i.e., 'having flowers in clusters').