Tim Bowen puts in another solid performance with this article.
Solid is mainly used as an adjective but it can also be used as a noun. In the singular, it is used to describe a substance that is not a liquid or a gas, and it can also be used to describe a shape that is three-dimensional and not flat. In the plural form, it can be used to describe solid food as opposed to liquids, as in ‘She’s been very ill since the operation and is still not able to eat solids’ or ‘Most babies are ready to eat solids when they have reached double their birth weight’.
As an adjective, apart from its regular meaning of firm, hard or strong, solid can also be used to mean completely good, with no mistakes or bad parts, as in ‘The team was fairly solid in defence’, ‘Will the evidence be solid enough to convince a jury?’ and ‘She gave another solid performance as an unemployed single mother’. If you describe a person as solid, you mean they are sensible and can be trusted, as in ‘He has a solid family background’ or ‘She’s a solid, reliable worker’. Solid can also be used to describe something that consists of one substance only, as in ‘a solid oak bookcase’ or ‘solid silver cutlery’.
Usually used after the noun, solid can also mean without any pauses or interruptions, as in ‘I can’t believe I slept for twelve hours solid’ or ‘It had been raining for three days solid and a number of rivers had burst their banks’. We can also talk about ‘solid rain’, but this should not be taken literally as rain is definitely liquid!