"Since" is simply a preposition which means "the period of time STARTING at the described moment". Similarly, "until" is a preposition which means "the period of time ENDING at the described moment".
since
prep.
自…以來(lái)； 自…以后
I have been there many times since the war.
自那次戰(zhàn)爭(zhēng)以來(lái),我曾去該地多次.
"Since then, he has developed another bad habit."
"自那以后,它養(yǎng)成了另一種環(huán)習(xí)慣."
"Since then, they have been trying to find out how the fire began."
"自那時(shí)以來(lái),他們一直在設(shè)法查明起火的原因."
詞性變化
conj.
自…以后； 自…以來(lái)
What have you been doing since I last saw you?
自我上次和你見(jiàn)面以后,你在做什么?
既然；因 為
Since you ask, I will tell you.
你既然問(wèn),我就告訴你.
"Since many of the customers work during the day, Billy has to collect the money at night."
"因?yàn)樵S多顧客白天上班,所以畢利只好晚上去收錢."
adv.
其后,后來(lái)
At first he refused but since has accepted.
他最初拒絕,但后來(lái)接受了.
We have been friends ever since.
自此以后我們一直是朋友.
"The fish, which has since been sent to a museum where it is being examined by a scientist, is called an oarfish."
"這條后來(lái)被送到一個(gè)博物館,在那里接受一位科學(xué)家的觀察、研究的魚(yú),名叫皇帶魚(yú)."
以前
How long since is it?
那是在多久以前?
until
prep., conj.
直到…為止
We can't go until Thursday.
我們要到星期四才能去.
I couldn't sew until I was six.
我直到六歲時(shí)才會(huì)用針縫東西.
We can't start the job until we have the approval from the authority concerned.
沒(méi)有有關(guān)當(dāng)局的批準(zhǔn)我們不能開(kāi)始這項(xiàng)工作.
He waited until the volcano became quiet and he was able to return two days later.
他一直等到火山平息下來(lái),兩天后他才得以重回火山上.
（亦作： till）