Roger replies:appropriate,suitable and adequate,sufficient,enough

appropriate ~ suitable

Appropriate and suitable are both qualitative adjectives - i.e. they describe the quality of something - and are very similar in meaning and usage. As you suggest, they carry the meaning of 'fitted, suited to a purpose.' They are both placed as modifiers before nouns and they are both used as complements after the verb be, although appropriate is perhaps more commonly used in this way, especially with the pronoun it. They are both used with the preposition for and are often used with negative prefixes. The adjectival form suitable (for) sometimes crops us in the verb format suited (to). Study the following examples:

• It is inappropriate to make jokes at funerals.
• It was inappropriate for her to joke with the Queen in such a light-hearted manner.
• The clothes she was wearing were quite unsuitable/inappropriate for the cold weather.
• Does this dress suit me? ~ Oh yes, it does. And it's very suitable/appropriate for formal occasions.
• It is a very violent film and is considered unsuitable/inappropriate for children to watch.
• I'm glad you praised him for that. It was an appropriate thing to do.
• He is just not suited to/suitable for this type of work.
• Such small flats are not really suitable for couples with young children. It is unsuitable/inappropriate accommodation.

adequate ~ sufficient ~ enough

Adequate, sufficient and enough are slightly different in meaning. If something is adequate, there is enough of it, but only just enough. If there is sufficient quantity of something, this suggests that there is as much of it as you need. Usage of these adjectives often denotes quantity rather than quality, whereas appropriate and suitable suggest a qualitative response to something. Study the following examples:

• The pay was adequate, but it certainly wasn't generous. The rate of pay - ?0 an hour - was barely adequate to raise a family on.
• His answer to the question was adequate but it wasn't developed sufficiently to gain high marks.
• The Prime Minister gave an inadequate reply to the journalist's question.
• The action taken to combat the spread of malaria was quite inadequate.
• There were not enough seats for all the guests. The supply of seats was quite inadequate.
• There was easily enough food for every one. There was a sufficient amount of food.
• There was insufficient evidence to convict him of house-breaking.