Definitions in relation to their use in kangaroo words, taken from Google Dictionary, and edited for formatting.
Kangaroo word: completionist
Joey word: completist
completionist (noun): a player who attempts to complete every challenge and earn every achievement or trophy.
completist (noun): an obsessive, typically indiscriminate, collector or fan of something.
The letters C, O, M, P, L, E, T, I, S, and T found within the kangaroo word “completionist” arrange in the listed order to complete the joey word “completist”. While a word can have multiple definitions, in relation to their use with kangaroo words, these two words share a similar meaning: a collector.