The word "OSTTL" is a combination of consonants and vowels that does not have a clear meaning in English. The spelling of this word can be explained using the International Phonetic Alphabet (IPA). The first letter "O" represents the open-mid back rounded vowel /ɔ/, while the next three letters "STT" make up the consonants /st/. The final letter "L" is the voiced alveolar lateral approximant /l/. Therefore, "OSTTL" can be pronounced as /ɔstl/.
As of my current knowledge and available resources, "OSTTL" does not appear to have an established or widely recognized dictionary definition. It seems to be an acronym that may represent specific jargon or a specialized term within a certain context or field. If you provide more context or background information, I would be glad to assist you further in understanding its meaning.