No, it is not (despite the LY ending). The word costly is an adjective (expensive, high-priced).
There are several reasons why a natural, gem-quality diamond is costly, the foremost being it's rarity. Only about 20% of all diamonds mined are gem-quality. Also, lab-created diamonds are less costly that natural diamonds. Industrial quality diamonds are not costly.
Cheap.
Dear,costly and high-priced are some of the synonyms for expensive.
costly
The superlative for costly is "most costly" or "costliest."
Yes, costly is an adjective. E.g. It was a costly mistake. (One that was expensive to fix, or that led to other bad consequences.)
Costly.
It should be most costly.
No Silicon is not costly. Pensil is of 3rupees in Pakistan
The opposite of costly can be cheap, inexpensive, or affordable.
The duration of Her Costly Affair is 1.6 hours.
Carlo Costly was born on 1982-07-18.
Anthony Costly was born on 1954-12-13.
Her Costly Affair was created on 1996-10-28.
Carlo Costly plays as a Forward for Honduras.
Ans: The costly material in concrete is cement