across-the-board vs extensive

across-the-board and extensive both are adjectives.

Word	Noun	Adjective	Verb	Adverb
across-the-board	No	Yes	No	No
extensive	No	Yes	No	No

As adjectives, across-the-board and extensive are synonyms defined as:

Other synonyms of across-the-board include all-embracing, all-encompassing, all-inclusive, blanket, broad, encompassing, panoptic, wide.

across-the-board (adjective)	extensive (adjective)
broad in scope or content	of agriculture; increasing productivity by using large areas with minimal outlay and labor
	broad in scope or content
	large in spatial extent or range or scope or quantity