There are a total of 28 10-letter words containing 'plex', and the number may vary in different dictionaries. You can specify the dictionary and order.

• amplexuses ₂₅
• apoplexies ₂₄
• cineplexes ₂₅
• complexest ₂₇
• complexify ₃₂
• complexing ₃₀
• complexion ₂₈
• complexity ₂₉
• fourplexes ₂₅
• googolplex ₂₆
• noncomplex ₂₉
• perplexing ₂₇
• perplexity ₂₆
• quadplexes ₃₂
• quadraplex ₃₂
• quadriplex ₃₂
• megaplexes ₂₂
• perplexers ₂₁
• plexiglass ₂₀
• triplexing ₂₀
• apoplexing ₂₂
• complexone ₂₃
• contraplex ₂₁
• implexions ₂₁
• implexuous ₂₁
• pleximeter ₂₁
• pleximetry ₂₄
• quadruplex ₂₉

There are 28 10-letter words containing plex in the well-known word game dictionary, 18 in the Scrabble US (US/Canada/Thailand - TWL/NWL) dictionary, and 25 in the Scrabble UK (International - SOWPODS/CSW) dictionary, and 16 in the Words with Friends (WWF) dictionary.