Not wanting to keep you waiting too long, here's Tim Bowen's article on the word long.

Apart from its use as an adjective (and occasionally as a verb – followed by for), the word long also functions as an adverb and, less frequently, as a noun.

As an adverb, its principal meaning is ‘for a long period of time’, as in ‘I hope you haven’t been waiting long' and ‘Smoking has long been linked to lung cancer’.

Used with before, after, ago and since, it can also mean much earlier or later than a particular event or period, as in ‘I knew her long before she became famous’, 'I was born long after my parents got married' and 'The time for negotiations has long since passed'. 

With time expressions such as day, week, month and year, long can be used to indicate the entire period, as in ‘I don’t think I could look after children all day long’ and ‘It was a miserable holiday; it rained all week long’.

The expression as long as (and its less common equivalent so long as) is used in the sense of 'provided that’ before stating the conditions that will make something else happen or be true, as in 'My parents don't care what job I do as long as I am happy'.

Used only in negative sentences or questions, long can follow the verb be to say or ask whether you will have to wait a long time for someone or something to be ready, arrive or happen, as in ‘Will you be long, or shall I wait?’ and ‘I’m just going to the shops I won’t be long’.

As a noun, long is also normally used in negatives and questions and means ‘a long period of time’. Examples of long functioning as a noun are ‘She joined the company in 1995, and before long she was promoted to sales manager’ and ‘Have you been married for long?’

if you long for something, you want it very much, as in, 'She longed for a cup of tea.'