Alkali
In chemistry, an alkali (; from Arabic: "al-qaly" "ashes of the saltwort") is a basic, ionic salt of an alkali metal or alkaline earth metal chemical element. An alkali also can be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The adjective alkaline is commonly, and alkalescent less often, used in English as a synonym for basic, especially for bases soluble in water. This broad use of the term is likely to have come about because alkalis were the first bases known to obey the Arrhenius definition of a base, and they are still among the most common bases.
Alkyl
In organic chemistry, an alkyl substituent is an alkane missing one hydrogen.
The term alkyl is intentionally unspecific to include many possible substitutions. 
An acyclic alkyl has the general formula CH. A cycloalkyl is derived from a cycloalkane by removal of a hydrogen atom from a ring and has the general formula CH.
Typically an alkyl is a part of a larger molecule. In structural formula, the symbol R is used to designate a generic (unspecified) alkyl group. The smallest alkyl group is methyl, with the formula CH−. Although the name 'alkyl' is strictly given to straight chain alkyls only. For branched chain alkyls, terms like "iso", "neo" are often used along with the word "alkyl".
The word root "alkyl" is encountered in several contexts. Alkylation is an important operation in refineries, for example in the production of high-octane gasoline. Alkylating antineoplastic agents refer to a class of compounds that are used to treat cancer. In such case, the term alkyl is used loosely. For example, nitrogen mustards are well-known alkylating agents, but they are more complex than a mere hydrocarbon. In chemistry, alkyl refers to a group, a substituent, that is attached to other molecular fragments. For example, alkyl lithium reagents have the empirical formula Li(alkyl), where alkyl = methyl, ethyl, etc. A "dialkyl" ether is an ether with two alkyl groups, e.g., diethyl ether (O(CH)). Alkyl also refers to an active ingredient in green algae preventatives used in swimming pools.