periphrasis (linguistics)
Definition - A device by which a grammatical relationship is expressed by an added word, instead of being shown by either inflection or derivation.

Example -

(1) I will leave tomorrow
(Here the future tense is formed by adding the auxiliary verb will, instead of it being formed by inflecting the verb itself).
(2) Ellen is more beautiful than Jane.
(Here the comparative is formed by adding the word more; as opposed to forming it with a suffix , e.g. Ellen is lovelier than Jane.)

Etymology -
The word derives from the Greek periphrazein, speak in a roundabout way (from peri, round about + phrazein, to express).

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