invaluable
adj.-
1 extremely useful (adj.) B2 Upper Intermediateextremely useful or important; having a value that is too high to measure.
having incalculable value; of such great utility or worth that it cannot be measured in monetary terms.
ExampleHer advice was invaluable when I was trying to choose a new career.
ExampleThe mentorship provided by the senior partners proved invaluable to the associates during the complex merger negotiations.
UsageUsually used to describe abstract things like help, advice, or information rather than physical objects.
Teacher's tipLearners often confuse this with 'worthless' because of the 'in-' prefix. Remind them it means the value is so high it cannot be calculated.
PitfallThe old car is invaluable, so I will sell it for ten dollars.The old car is worthless, so I will sell it for ten dollars.The prefix 'in-' here means 'beyond' or 'cannot be', not 'not'. 'Invaluable' means extremely valuable, while 'worthless' means having no value.
From in- + valuable (compare priceless).