Triclosan binds to bacterial enoyl-acyl carrier protein reductase
(ENR) enzyme, which is encoded by the gene FabI. This binding
increases the enzyme's affinity for nicotinamide adenine dinucleotide
(NAD+). This results in the formation of a stable, ternary complex of
ENR-NAD+-triclosan, which is unable to participate in fatty acid
If you notice, you would see that this mechanism is attributed to low concentrations of triclosan when it acts as a bacteriostatic. Disinfectants, IMO cause direct chemical damage to cell (denaturation of proteins/destruction of the membrane etc) unlike antibiotics which inhibit some vital metabolic processes. Triclosan is generally used in the form of a disinfectant (at high concentrations). Even though its enzyme inhibitory properties have been studied, it is not systemically administered in the form of an antibacterial drug.
The terms antibiotics and bactericidal were coined when mechanisms were not really known. Even then, antibiotic is traditionally known as a substance that is produced by one organism (a fungus in case of penicillin) to prevent the growth of the other.
I would like to differ from Christiaan's opinion that antibiotics are substances against which resistance can be developed. It is possible to acquire resistance towards a conventional, broad spectrum, direct damage agent. For instance there are bacteria that can survive heat/UV/γ-rays (which are physical disinfectants). Microbes can also develop resistance to chemical agents and though I cannot cite an example at the moment, I can think about how the cell can achieve it. One way is to develop a stronger cell wall.
Also note that alcohol is not considered a disinfectant at concentrations < 70%. At much lower concentrations alcohol can actually serve as an energy source.
So I think this is the tacitly accepted definition:
Disinfectants are usually synthetic chemicals that inflict direct damage whereas antibiotics are primarily natural chemicals that inhibit some vital metabolic process.
The term bactericidal or biocidal denotes the consequence rather than the nature of the mechanism. Antibiotics can be bactericidal too. Many herbicides are inhibitors of chloroplastidial metabolism.