From BiblePortal Wikipedia

Vine's Expository Dictionary of NT Words [1]

1: Πολύς (Strong'S #4183 — Adjective — polus — pol-oos' )

"much," is rendered "plenteous" in  Matthew 9:37 , of a harvest of souls, and  Luke 10:2 , RV (AV, "great"). See Great.

King James Dictionary [2]

PLEN'TEOUS, a. from plenty. Abundant copious plentiful sufficient for every purpose as a plenteous supply of provisions a plenteous crop.

1. Yielding abundance as a plenteous fountain.

The seven plenteous years.  Genesis 41

2. Having an abundance.

The Lord shall make thee plenteous in goods.  Deuteronomy 28

3. Possessing in abundance and ready to bestow liberally.

 Psalms 86

This word is less used than plentiful.

Webster's Dictionary [3]

(1): ( a.) Yielding abundance; productive; fruitful.

(2): ( a.) Having plenty; abounding; rich.

(3): ( a.) Containing plenty; abundant; copious; plentiful; sufficient for every purpose; as, a plenteous supply.