Giving or providing energy and vitality; causing someone to feel invigorated and enthusiastic (British spelling, American 'energizing').
From energise + -ing (present participle suffix, from Old English -ung/-ing, originally a noun suffix that became generalized for participles). British spelling maintains the -s- throughout.
The -ing ending is one of English's busiest suffixes—it works as a noun (running is fun), adjective (that's energising!), and verb form, showing how English compresses multiple grammatical functions into single words.
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