wastefulEnglishOxford American Thesauruswasteful adjective wasteful use of energy in the home: prodigal, profligate, uneconomical, extravagant, lavish, excessive, careless, imprudent, improvident, reckless; thriftless, spendthrift, squandering; needless, useless, not needed, squandered. ▷antonyms thrifty, frugal.