Cases of word usage

1) urgent; essential (imperative)

2) (of value, quality) belonging to, existing within, what is essential and natural (not caused or produced from outside) (intrinsic)

3) the commonest metal (symbol Fe), used in manufacturing and building, an also forming an essential part of blood; a flat-bottomed implement heated and used for smoothing clothes etc (iron)

4) something that it is essential to see, do, hear etc; (used to express an obligation or an order) (must)

5) a chemical substance that is an essential part of all living cells (nucleic acid)

6) that is requested by law; essential (obligatory)

7) any part of an animal body or plant with an essential purpose; the means of getting something done; a musical instrument with a keyboard, from which sounds are produced by air forced through pipes (organ)

8) the soft, white substance that fills the stems of some plants and trees; an essential part (of something) (pith)

9) exactly; to find the essential or basic cause or reason of (something) (plumb)

10) any of a number of organic substances which are present in certain foods and are essential to the health of people and animals (vitamin)